Low-temperature synthesis of nanoparticle-assembled, transparent, and low-crystallized hydroxyapatite blocks

The mesoporous carbon CMK-3 adsorbent was prepared, characterized, and used for the removal of anionic methyl orange dye from aqueous solution. Adsorption experiments were carried out as batch studies at different contact time, pH, initial dye concentration, and salt concentration. The dye adsorption equilibrium was rapidly attained after 60 min of contact time. Removal of dye in acidic solutions was better than in basic solutions. The adsorption of dye increased with increasing initial dye concentration and salt concentration. The equilibrium data were analyzed by the Langmuir and Freundlich models, which revealed that Langmuir model was more suitable to describe the methyl orange adsorption than Freundlich model. Experimental data were analyzed using pseudo-first-order and pseudo-second-order kinetic models. It was found that kinetics followed a pseudo-second-order equation. Thermodynamic study showed that the adsorption was a spontaneous and exothermic process.     

Quartzite an efficient adsorbent for the removal of anionic and cationic dyes from aqueous solutions

Quartzite obtained from local source was investigated for the removal of anionic dye congo red (CR) and cationic dye malachite green (MG) as an adsorbent from aqueous solution in batch experiment. The adsorption process was studied as a function of dye concentration, contact time, pH and temperature. Adsorption process was described well by Langmuir and Freundlich isotherms. The adsorption capacity remained 666.7 mg/g for CR dye and 348.125 mg/g for MG dye. Data was analyzed thermodynamically, ΔH⁰ and ΔG⁰ values proved that adsorption of CR and MG is an endothermic and spontaneous process. Adsorption data fitted best in the pseudo-first order kinetic model. The adsorption data proved that quartzite exhibits the best adsorption capacity and can be utilized for the removal of anionic and cationic dyes.     

化学改性麦壳对孔雀绿的吸附作用

通过不同的化学方法对农业副产物麦壳进行改性,以制得廉价的生物吸附剂,并分别研究了它们对孔雀绿的吸附性能。结果表明,天然麦壳对孔雀绿有一定的吸附量,经化学修饰后对孔雀绿的吸附量有不同程度的提高,其中,经硝酸酸化后的麦壳对孔雀绿的吸附效果最好。通过研究硝酸改性麦壳吸附孔雀绿条件的影响发现,吸附40min达到平衡;随初始浓度增加,吸附量增大;溶液在中性或碱性范围内,吸附量较高;吸附符合Langmuir和Freundlich等温模型,吸附动力学过程可以用准二级动力学方程来较好地拟合。因此,硝酸改性麦壳可以用于有效去除水体中的孔雀绿。     

Adsorption of methylene blue dye from aqueous solution by agricultural waste: Equilibrium,thermodynamics, kinetics,mechanism and process design

The adsorption of methylene blue (MB) dye from aqueous solution onto a cashew nut shell (CNS) was investigated as a function of parameters such as solution pH, CNS dose, contact time, initial MB dye concentration and temperature. The CNS was shown to be effective for the quantitative removal of MB dye, and the equilibrium was reached in 60 min. The experimental data were analysed by two-parameter isotherms (Langmuir, Freundlich, Temkin and Dubinin-Radushkevich models) using nonlinear regression analysis. The characteristic parameters for each isotherm and the related correlation coefficients were determined. Thermodynamic parameters such as ΔG°, ΔH° and ΔS° were also evaluated, the sorption process was found to be spontaneous and exothermic. Pseudo-first-order, pseudo-second-order and Elovich kinetic models were used to analyze the adsorption process. The results of the kinetic study suggest that the adsorption of MB dye matches the pseudo-second-order equation, suggesting that the adsorption process is presumably chemisorption. The adsorption process was found to be controlled by both surface and pore diffusion. Analysis of adsorption data using a Boyd kinetic plot confirmed that the external mass transfer is a rate determining step in the sorption process. A single-stage batch adsorber was designed for different CNS doses to effluent volume ratios using the Freundlich equation. The results indicated that the CNS could be used effectively to adsorb MB dye from aqueous solutions.     

Adsorptive removal of malachite green and Rhodamine B dyes on Fe3O4/activated carbon composite

This study demonstrates the adsorption experiments of toxic dyes malachite green (MG) and Rhodamine B (RB) on Fe₃O₄-loaded activated carbon (AC). AC, which is known to be a high-capacity adsorbent, was aimed to be easily separated from aqueous media by loading it with Fe₃O₄. Fe₃O₄-loaded AC was prepared by the coprecipitation method and named magnetic activated carbon (M-AC), and the produced M-AC was characterized by x-ray diffraction (XRD), thermogravimetric analysis (TGA), and pH_pzc analyses. MG and RB adsorption by the M-AC was performed separately by batch technique and the effects of adsorbent amount, solution pH, and initial dye concentration on the adsorption were explored. Maximum removal efficiencies were found to be 96.11% for MG and 98.54% for RB, and the Langmuir isotherm model was the most fitted isotherm model for the adsorption. The kinetic and thermodynamic studies showed that the adsorption proceeded via the pseudo-second-order kinetic model and endothermic in-nature for both dyes.     

Removal of cationic methylene blue and malachite green dyes from aqueous solution by waste materials of Daucus carota

In present study adsorption capacity of waste materials of Daucus carota plant (carrot stem powder: CSP and carrot leaves powder: CLP) was explored for the removal of methylene blue (MB) malachite green (MG) dye from water. The morphology and functional groups present were investigated by scanning electron microscope (SEM) and Fourier transform infrared (FTIR) spectroscopy. The operating variables studied were pH, adsorbent dose, ionic strength, initial dye concentration, contact time and temperature. Equilibrium data were analysed using Langmuir and Freundlich isotherm models and monolayer adsorption capacity of adsorbents were calculated. Kinetic data were studied using pseudo-first and pseudo-second order kinetic models and the mechanism of adsorption was described by intraparticle diffusion model.Various thermodynamic parameters such as enthalpy of adsorption ΔH°, free energy change ΔG° and entropy ΔS° were estimated. Negative value of ΔH° and negative values of ΔG° showed that the adsorption process was exothermic and spontaneous. Negative value of entropy ΔS° showed the decreased randomness at the solid–liquid interface during the adsorption of MB and MG onto CSP and CLP.     

Removal of malachite green by adsorbents from paper industry waste materials

The objective of this work is to study the removal of malachite green (MG) from water by adsorbents obtained from pyrolysis of two paper industry waste materials: one de-inking paper sludge (HP) and one organic sludge from virgin pulp mill (RT). Both adsorbents showed elevated MG removal. Maximum adsorption Q ₀ obtained by Langmuir equation was higher for the adsorbent from HP (HP-3, 982 mg/g) than RT (RT-3, 435 mg/g). However, K _L (Langmuir) and 1/n (Freundlich) indicated that affinity and intensity of adsorption is higher for the adsorbents from RT. Thermal analysis (TG, DTG and DTA) of adsorbents before and after MG removal was performed in N₂ atmosphere.     

Amorphous titanium dioxide as an adsorbent for dye polluted water and its recyclability

Amorphous TiO₂, synthesized from TiCl₄ and diluted NH₃ solution, was characterized by X-ray diffraction spectrometry, UV–Vis diffused reflectance spectroscopy, Fourier-transformed infrared spectroscopy, and scanning electron microscopy. The powder exhibited high specific surface area at 508 m²/g as measured by the Brunauer-Emmett-Teller method. The pH at point of zero charge of the as-prepared amorphous TiO₂ was determined by the pH drift method to be 6.8. The product was studied for its sorption efficiency using two dyes—crystal violet (CV) and malachite green (MG). Studies on the effects of various sorption parameters (contact time, TiO₂ dosage, pH of solution, and initial concentration of dye) were carried out in order to find the optimum adsorption conditions for which the results were: contact time ~30 min, TiO₂ dosage ~0.05–0.1 g, pH 7–9, and initial concentration <1 × 10^?4 M. The adsorption data were analyzed and fitted better with the Langmuir model than the Freundlich model. The maximum adsorption capacities obtained from the Langmuir model were 0.4979 and 0.4075 mmol dye/g TiO₂ for CV and MG dye, respectively. In addition, the regeneration and the recyclability of the prepared amorphous TiO₂ were also studied. The used adsorbent should be regenerated 10–12 h before reuse in the next cycle for the best result.     

Removal of the Malachite Green (MG) Dye From Textile Industrial Wastewater Using the Polyurethane Foam Functionalized with Salicylate

Polyurethane foam was chemically functionalized with salicylate through the –N?N– group generating a stable chelating sorbent PUFSalicylate (PUFS) for being used as a low cost, available, and renewable adsorbent for the removal of Malachite Green (MG) textile dye from aqueous solutions. Batch experiments were carried out for sorption kinetics and isotherms. The synthesized adsorbent was characterized by Fourier Transform Infrared Spectroscopy (FTIR), scanning electron microcopy (SEM), and X-ray diffraction. The present study is related to the removal of colorants. Adsorption of MG dye on PUFS was studied as a function of different experimental parameters such as temperature, contact time, amount of adsorbent, and pH. A spectrophotometer technique was used for measuring the extent of adsorption. The data were fitted with Langmuir and Freundlich isotherm equations and their corresponding constants were calculated from the slopes and intercepts of their respective lines. From the measured adsorption isotherms at different temperatures 298, 308, and 318 K, it was found that adsorption increases as the temperature increases within this range. The measured adsorption amount of MG dye increases with increased pH.     

The effect of surface modification of mesoporous carbons on Auramine-O dye removal from water

Mesoporous carbon of regular structure was subjected to oxidation by ammonium persulfate at 30, 60 or 100 °C. The mesostructure and pore evolution were characterised by XRD, TEM, and N₂ sorption techniques. The functional groups present on the surface of the carbon materials were identified by FTIR and thermogravimetric studies. It was established that the micropores and small mesopores could be blocked by the surface oxides attached under mild oxidation. High densities of surface oxygen complexes, especially carboxylic groups, were generated on the surface of mesoporous carbons. All materials obtained were tested for the removal of Auramine-O from aqueous solution. Adsorption experiments were carried out as batch studies at different contact time, pH and initial dye concentration. Removal of this cationic dye in basic solutions was more effective than in acidic solutions. The highest sorption capacity towards Auramine-O was obtained for the carbon sample oxidised by ammonium persulfate solution at 100 °C. Fitting equilibrium data to Langmuir and Freundlich isotherms showed that Langmuir model was more suitable to describe the Auramine-O adsorption. The changes in standard enthalpy (ΔH⁰), standard entropy (ΔS⁰) and Gibbs free energy (ΔG⁰) were analysed. Thermodynamic study showed that the adsorption of Auramine-O was a spontaneous and exothermic process.     

Garlic Root Biomass as Novel Biosorbents for Malachite Green Removal: Parameter Optimization,Process Kinetics and Toxicity Test

The potential of the agricultural waste garlic root to remove malachite green(MG) from aqueous solutions was evaluated. The adsorption of this dye onto garlic root was confirmed by means of Fourier transform infrared analysis(FTIR) and scanning electron microscopy(SEM). The equilibrium data fitted well into the Langmuir mo- del(R²>0.99), and the adsorption kinetics followed the pseudo-second-order equation(R²>0.99). The maximum adsorption capacities of MG onto the adsorbent were 172.41 and 232.56 mg/g with the addition of 1 and 2 g/L garlic root, respectively. The optimal conditions for MG removal were established on the basis of orthogonal experiments(OA₁₆ matrix). The concentrations of both MG and garlic root significantly affected the removal efficiency. The acute toxicity test indicated that the treated MG solutions were less toxic than the parent solutions. These results suggest that garlic root is a potential low-cost adsorbent for removing dye from industrial wastewater.     

Removal of copper from aqueous solution by aminated and protonated mesoporous aluminas: kinetics and equilibrium

A novel adsorbent, aminated and protonated mesoporous alumina, was prepared and employed for the removal of copper from aqueous solution at concentrations between 5 and 30 mg/l, in batch equilibrium experiments, in order to determine its adsorption properties. The removal of copper by the adsorbents increases with increasing adsorbent dosages. The adsorption mechanism is assumed to be an ion exchange between copper and the hydrogen ions present on the surface of the mesoporous alumina. The adsorbent was characterized by XRD, TEM, SEM, and BET methods. The sorption data have been analyzed and fitted to linearized adsorption isotherm of the Freundlich, Langmuir, and Redlich-Peterson models. The batch sorption kinetics have been tested for first-order, pseudo-first-order, and pseudo-second-order kinetic reaction models. The rate constants of adsorption for all these kinetic models have been calculated. Results also showed that the intraparticle diffusion of Cu(II) on the mesoporous catalyst was the main rate-limiting step.     

Kinetics and adsorption equilibrium in the system aqueous solution of copper ions—granulated activated carbon

The feasibility of using granulated activated carbon for adsorption removal of copper from aqueous solution was studied. The influence of pH, amount of the adsorbent, contact time, and copper concentration on adsorption of copper was investigated. The single-component equilibrium data on copper adsorption were analyzed using the Langmuir, Freundlich, Redlich—Peterson, Temkin, and Toth adsorption isotherms. The adsorption process was followed by two simplified kinetic models including pseudo-first- and pseudo-second-order equations. Kinetic parameters, rate constants, equilibrium sorption capacities, and the corresponding correlation coefficients were calculated and examined for each kinetic model. It was shown that copper adsorption can be described by the pseudo-second-order equation.     

Kinetics and equilibrium studies of adsorption of chromium(VI) ion from industrial wastewater using Chrysophyllum albidum (Sapotaceae) seed shells

A new biosorbent has been prepared by coating Chrysophyllum albidum (Sapotaceae) seed shells with chitosan and/or oxidizing agents such as sulfuric acid. This study investigated the technical feasibility of activated and modified activated C. albidum seed shells carbons for the adsorption of chromium(VI) from aqueous solution. The sorption process with respect to its equilibria and kinetics as well as the effects of pH, contact time, adsorbent mass, adsorbate concentration and particle size on adsorption was also studied. The most effective pH range was found to be between 4.5 and 5 for the sorption of the metal ion. The pseudo-first-order rate equation by Lagergren and pseudo-second-order rate equation were tested on the kinetic data, the adsorption process followed pseudo-second-order rate kinetics, also, isotherm data was analyzed for possible agreement with the Langmuir and Freundlich adsorption isotherms, the Freundlich and Langmuir models for dynamics of metal ion uptake proposed in this work fitted the experimental data reasonably well. However, equilibrium sorption data were better represented by Langmuir model than Freundlich. The adsorption capacity calculated from Langmuir isotherm was 84.31, 76.23 and 59.63 mg Cr(VI)/g at initial pH of 3.0 at 30 °C for the particle size of 1.00–1.25 mm with the use of 12.5, 16.5 and 2.1 g/L of CACASC, CCASC and ACASC adsorbent mass, respectively. This readily available adsorbent is efficient in the uptake of Cr(VI) ion in aqueous solution, thus, it could be an excellent alternative for the removal of heavy metals and organic matter from water and wastewater.     

Synthesis of carboxyl‐functionalized magnetic nanoparticles for adsorption of malachite green from water: Kinetics and thermodynamics studies

Magnetic carboxyl‐coated silica iron oxide nanoparticles (Fe₃O₄@SiO₂‐COOH NPs) were successfully synthesized, characterized, and then applied as a nano‐adsorbent for removal of malachite green (MG) from aqueous solutions. According to the experimental results, about 97.5% of MG could be removed from aqueous solutions using an adsorbent amount of 0.5 g/L at pH = 9 in 120 min. The kinetics and equilibrium adsorptions is well‐described by the pseudo‐second‐order kinetics and Langmuir model with the maximum absorption capacity of 263.16 mg/g, respectively. Thermodynamic studies showed that the adsorption of the hazardous MG dye was spontaneous and endothermic with a random process.     

Adsorption and desorption kinetics of benzene derivatives on mesoporous carbons

Adsorption and desorption of benzoic and salicylic acids and phenol from a series of synthesized mesoporous carbons is measured and analyzed. Equilibrium adsorption isotherms are best described by the Langmuir–Freundlich isotherm. Intraparticle diffusion and McKay’s pore diffusion models, as well as mixed 1,2-order (MOE), integrated Langmuir kinetic equation (IKL), Langmuir–Freundlich kinetic equation and recently derived fractal-like MOE (f-MOE) and IKL models were compared and used to analyze adsorption kinetic data. New generalization of Langmuir kinetics (gIKL), MOE and f-MOE were used to describe desorption kinetics. Analysis of adsorption and desorption half-times shows simple relation to the size of carbon pores.     

Adsorption characteristics of malachite green dye onto novel kappa-carrageenan-g-polyacrylic acid/TiO2–NH2 hydrogel nanocomposite

Batch adsorption experiments were carried out for the removal of malachite green (MG) cationic dye from aqueous solution using novel hydrogel nanocomposite that was prepared by graft copolymerization of acrylic acid (AA) onto kappa-carrageenan (κC) biopolymer in the presence of a crosslinking agent, a free radical initiator and aminosilica-functionalized TiO₂ nanoparticles (κC-g-PAA/TiO₂–NH₂). The factors influencing adsorption capacity of the adsorbents such as initial pH value (pH₀) of the dye solutions, TiO₂–NH₂ content (wt%), initial concentration of the dye, amount of adsorbents, and temperature were investigated. The adsorption capacity of hydrogel nanocomposite for MG was compared with hydrogel. The adsorption behaviors of both adsorbents showed that the adsorption kinetics and isotherms were in good agreement with a pseudo-second-order equation and the Langmuir equation. The high adsorption capacity (q _m= 666–833 (mg/g)) and the favorable heterogeneity factor (n = 1.2–1.5) calculated from isotherm equations show the efficiency of the novel adsorbents.